This is used in Merseyside and is a derogatory term used for someone who tends to fancy women (or men) who are not nice looking in any way shape or form. However, a shallow-hall effect takes place which distorts the connection between the eyes and the brain, causing them to completely misinterpret what they see, hence finding an unattractive person rather nice looking.

Wilko lad, oh my god i cant believe you are even lookin' at her kid, you're a lil brewbat u lad